What's the diference between Aedra and Daedra, why Meridia and Azura aren't considered Aedras since they are good.. etc.. etc..
Aedra and Daedra are essentially the same, however Aedra have invested some portion of their power in the creation of Mundas/Nirn whereas Daedra have not. Because of this Aedra are generally weaker then their Daedra cousins but they also act as a barrier limiting the amount of influence the Daedra have in Nirn.
There are a couple of gods that are not Aedra or Deadra:
- notably Anu and Padomay (A.K.A Sithis) are neither, They are not so much spirits/plane gods like the Aedra/Deadra as they are personifications of forces even stronger then the Aedra and the Deadra. Possibly strong enough that they could kill any deadra or aedra that would dare enter their domains.
- Mortals who have become gods are neither (Talos, Tribune, Mannimarco/God of Worms*, the 2nd Sheogorath and a few others)
When you get into it, essentially Anu and Padomay created the universe as it is. The Deadra and Aedra are spirits that achieved godhood and then went on to form planes/planets of their own. Mortals are likely the descendants of Aedra who invested too much power in the creation of Nirn and lost their divinity and so knew they had to reproduce or die out entirely. Lorkhan himself invested ALL of his power in the creation of Nirn and died.
Also the 8 divines are not the only Aedra, Magnus maybe considered an Aedra but he withdrew from the process of creation of Nirn and during this he ripped a hole in the fabric of space between Oblivion and Aetherius creating the Sun, also called Magnus. Mortals are able to use Magnus' power in the form of magic.
*not to be confused with the King of Worms in Oblivion, they were originally one in the same but were split into two different beings when Mannimacro(god of worms) achieved godhood